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I was wondering why (desktop) motherboards have 4 slots for RAM. I know that one can use fewer RAM sticks, and that server motherboards have more slots, but I could not find a satisfying answer to why there are four (but not more than that.)

Is it a limitation of the CPU?

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  • Its a limitation of the ram and the memory controller. More slots equals more capacitive load equals lower speed. You normally have a multiple of 2 slots in order to have a double width memory bus.
    – Kartman
    Commented Oct 12, 2021 at 12:54
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    Some desktop motherboards do have more than 4 slots, so the question is just based on false assumption that they don't exist.
    – Justme
    Commented Oct 12, 2021 at 12:59
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    I was wondering, why (desktop) motherboards have 4 slots of ram. Hmm, how about this desktop motherboard with 8 slots: asus.com/uk/Motherboards-Components/Motherboards/All-series/… ? The reason why most MBs have 4 slots might have to do with price, most users don't need more than 4 slots and/or are unwilling to pay for more than 4 slots. Check the price of that 8-slot board and see for yourself (OK, that MB is very high end, lots of features but still, a 4 socket board will be much cheaper)!
    – Bimpelrekkie
    Commented Oct 12, 2021 at 13:01
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    26 alone with AMD processors: Newegg
    – StainlessSteelRat
    Commented Oct 12, 2021 at 15:54
  • I posit that more then 4 slots is a tradeoff of cost/size/added value. As the amount of memory is limited by the CPU, and each slot takes space, requires testing and could increase power and complexity its not warranted in most cases.
    – davidgo
    Commented Oct 13, 2021 at 2:16

2 Answers 2

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Why does there need to be more than four RAM slots in a low-end consumer PC? As the consumers' need for RAM gets bigger the size range of the RAM sticks on the market gets bigger at the top end too, so there's already sufficient RAM capacity in four RAM slots for a budget PC. Let's say a consumer has a motherboard with 4 slots and each slot supports up to 16GB RAM. A typical consumer needs far less than 64GB RAM, so why should the consumer pay for more RAM than he needs?

In the case of medium- and high-end motherboards, some of these motherboards have 6 or more RAM slots. There's a theoretical limitation to the amount of RAM a motherboard can have, but this upper limit is far higher than a typical home PC user would ever encounter. The new Mac Pro model expected to be launched in 2022 will offer an option to be shipped with 128GB unified memory. Apple's new M1 Pro SoC places unified memory beside the other fundamental components, all on the same silicon. This results in faster memory bandwidth for both the CPU and the graphics card. source

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  • In the comments above,the question was clarified more: for example, take motherboard for Intel LGA1200. Why doesn't it have more than 4 slots of ram. I'm well aware about the amount of memory that is supported, but since dual channel memory controller can be used with 4 sticks, why not split it to more, for example 8 or 16? so the question is not about memory size, but the physical slots. and we'll leave the high end motherboards out of this, since the same question can be directed to that: " why there are not more than <insert amount of slots that can be found with google> slots of ram?"
    – Quirosaur
    Commented Nov 29, 2021 at 9:04
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  • The speed at which the electrons travel, can't make it faster. We need the RAM to be as close as possible to the CPU, and addition of any distance is not good.
  • Then we have the memory channels, if a CPU has N memory channels, then an ideal number of DDR slots will be the same N. If we have 2 memory channels and 4 DDR slots, we are really pushing it, things just ought to be slower.
  • If it's important to have more DDR slots than the number of memory channels, go with "Daisy Chain" type of connection of the slots. We also have "T-Topology" but it's not as fast.
  • Such systems where we have more DDR slots than memory channels also create constraints for us, such as fill this and this slot first, otherwise it won't work. It has to do with the reflection noise signals create when they operate at high frequencies.
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    Commented Oct 8, 2023 at 6:31

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